OTTAWA — Some residents returned to Fort McMurray, Alberta, on Wednesday for the first time since wildfires forced them out and ravaged their city four weeks ago. But it was hardly a triumphant homecoming, as the city’s gradual reopening came amid concerns that it was premature.

The returning residents, identified by government-issued wristbands, were watched over by more than 300 officers of the Royal Canadian Mounted Police and were given a long list of warnings. Officials told them to keep their gas tanks topped off, and to take at least two weeks’ worth of food, water, medicine and other essentials with them, because stores and other services in the city have not fully reopened.

And many of the 88,000 evacuees have been told that it is still not safe for them to return: older people, children under 7, pregnant women and people with any of a variety of medical conditions.

The city’s tap water is not drinkable yet, and may not be available for weeks. Other utilities are not back online, either.

Many of those who did return on Wednesday were not expected to stay long. Rather, they will most likely check on their homes, retrieve personal items left behind in the haste of evacuation and head south again to await the restoration of something closer to normal life.

It may be a long wait. Environmental experts say the ash left by the fire is so caustic and full of toxins that many surviving houses in the worst-hit neighborhoods must be sealed off, probably until September.

Given all that, some residents, including members of the local City Council, have questioned the timing of the return. But as crews continued to spray sealant over the ash and rubble, provincial government officials repeatedly assured the public that many people could return safely, if not conveniently.

“Personally, I would feel quite comfortable to go back,” Scott Long, the executive director of the Alberta Emergency Management Agency, told reporters on Tuesday at a news conference. “We didn’t work this hard to make sure that people are safe, to bring them back to an unsafe area and leave them to their own devices.”

Rachel Notley, the premier of Alberta, agreed with Mr. Long’s analysis but warned that returning may not be easy.

She observed that, after the panicked evacuation of the city, when some residents drove through tunnels of flame, “it is very possible that the re-entry process will be the next most stressful day.”

Ms. Notley, who has visited the city twice since the fire broke out, added, “I think it will be shocking.”

Provincial officials have said that the government underestimated the emotional and psychological effects of another major fire in 2011, which forced about 7,000 people to evacuate the town of Slave Lake, Alberta, and which ultimately destroyed about one-third of the community. So this time, mental health workers from across Canada have been arriving in Alberta over the past few weeks to help the Fort McMurray evacuees.

The wildfire that scorched the city remains out of control and now covers about 1.4 million acres. But for some time, the flames have been moving away from Fort McMurray, deep into largely unpopulated woodlands, and there is little unburned forest left near the city to provide a path for the flames back toward town.

As residents retraced the evacuation route up Highway 63, the route to the city, they were greeted by firefighters who had parked two fire trucks on an overpass and suspended a giant Canadian flag, bracketed by provincial and municipal flags, on a rope tied between their raised ladders.

Three neighborhoods of Fort McMurray were particularly devastated by the fire. After laboratory analysis of the ash and debris there, some 567 surviving houses and a dozen apartments in or near those neighborhoods have been declared unfit for habitation until a cleanup can be completed.

In all, 1,921 buildings were destroyed and 174 damaged by the fire, about 10 percent of the structures in the city. Judging by what could be seen by reporters on a recent tour, the vast majority of lost structures were houses or apartments.

Up to 15,000 people were allowed to return beginning on Wednesday, in a gradual process that will continue until Saturday. The most immediate concerns for many will be documenting damage for insurance claims and dealing with rotting food left behind in unpowered refrigerators and freezers. The provincial government has been working with a railroad on a plan for removing masses of appliances contaminated by spoiled food.

And while much of the ground in and around the city is blackened and charred, some homeowners in the least-affected parts of town were beating down overgrown lawns on Wednesday.

The reopening of the city comes at a time when insurance reimbursements for hotel stays are drying up for many evacuees. Heather Mack, director of government relations for the Insurance Bureau of Canada, an industry group, told reporters on a conference call that coverage for hotel expenses typically runs out after 14 to 30 days. The province has set up a fund to assist evacuees with housing costs that insurance does not cover.

Many of those who fled the city have vowed to rebuild. But an economic slump in Alberta, brought about by low oil prices, has led to many job losses and has limited opportunities in what had been Canada’s boom town.

While some homeowners may be required under the terms of their mortgages to rebuild their homes, Ms. Mack said, many others will be free to take a cash settlement and walk away.

“There’s some people who might choose that,” she said. “Somebody who’s close to retirement and may want to settle elsewhere.”

A version of this article appears in print on , on Page A8 of the New York edition with the headline: First Residents Return to Fort McMurray After Fire. Order Reprints | Today’s Paper | Subscribe

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